The present invention relates generally to heat exchanger assemblies and more particularly to such heat exchanger assemblies employed as evaporator assemblies in ice making machines. The present invention also relates to a method of fabricating such heat exchanger or evaporator assemblies.
Various types of heat exchanger assemblies, including evaporator assemblies for ice making machines frequently include a wall composed of a heat transmissive material and a plurality of sections of spaced-apart elongated fluid conduits, also composed of a heat transmissive material, disposed on one side of the wall for conveying a heat transfer fluid therethrough in order to transfer heat between the heat transfer fluid in the fluid conduits and the opposite side of the wall. The heat transfer efficiency of such heat exchanger assemblies is largely dependent upon the area of contact for conductive heat transfer between the fluid conduits and the heat transmissive wall. Such heat transfer efficiency is especially important in ice making machines with evaporator assemblies having a generally cylindrical evaporator tube and a helical fluid conduit positioned on the exterior wall of the evaporator tube with axially adjacent turns of the helical fluid conduit being axially spaced apart from one another. In such ice making machines, the heat transfer efficiency of the evaporator assembly has a very significant bearing upon the quantity of ice that the ice making machine is capable of producing in a given time as well as the cost of operating the ice making machine.
In the above-mentioned prior ice making machines, as well as in other heat exchanger devices, the adjacent turns or sections of the fluid conduits are spaced apart from one another and are typically of a cross-sectional shape having generally arcuate sides. Thus the area of contact between the fluid conduit and the heat transmissive wall is typically limited to a relatively small percentage of the outer surface areas of the heat transmissive wall and the fluid conduits, thus resulting in a relatively small heat transmissive conduction or contact area therebetween. Various attempts have been made to increase the area of contact, and thus the area of the heat conductive path, between the heat transmissive wall and the fluid conduits or arcuate conduit sections.
While such previous attempts have met with varying degrees of success, they have either not been fully effective in maintaining the area of contact, and thus the heat conductive path, between the fluid conduit and the heat transmissive wall, or they have done so only by resorting to inordinately complex structures that are difficult and relatively expensive to manufacture and install.
An object of the present invention is to improve the area of contact, and thus the heat conductive path, between a fluid conduit or conduit sections at a heat transmissive wall in an evaporator assembly or other heat exchanger device.
A further object of the present invention is to provide such an improved heat exchanger or evaporator assembly that is relatively simple and inexpensive to manufacture and install, and that thus provides an optimized relationship between efficient heat transfer, simplicity, and economy.
A further object of the present invention is provision of an apparatus whereby a straight section of copper tubing of circular cross-section may efficiently be formed into a cross-section having a D-shaped configuration with the flat of the "D" advantageously providing for enhanced surface contact with the outside transmissive surface of the evaporator cylinder.
In accordance with the present invention, an improved heat exchanger assembly has a cylindrical wall composed of a heat transmissive material and a fluid conduit, also composed of a heat transmissive material, coiled about the exterior surface of the wall for conveying a heat transfer fluid therethrough. The fluid conduit forms a continuously extending cylindrical annulus with the space between adjacent pairs of the coiled fluid conduit sections being held to a minimum because of the "D" shape, with the flat of the "D" enhancing heat transfer between the heat transmissive materials.
In accordance with this invention, the linear fluid conduit is formed on a specially configured apparatus into a cylindrical helix with the tube so coiled having a D-shaped cross-section, which helix is then inserted about the outside of the heat exchanger cylinder and the flattened wall of the deformed tube engaging flush with the exchanger. The apparatus for making the tube comprises a cylindrical coil mandrel upon which the tube is simultaneously coiled and axially spaced and a coil wheel assembly comprising a vertically adjustable support frame having a pair of upstanding arms between which a coil wheel is rotatably supported. The cylindrical surface of the coil mandrel is for flattening one side of the tube and the outer periphery of the wheel is configured with a semi-circular groove for engaging the other side of the tube cross-section.
In the formation of the helix, the tube is axially inserted into a narrowed throat formed between the coil mandrel and the coil wheel causing the tube to be simultaneously deformed into a D-shaped cross-section and wrapped into a helix about the coil mandrel. The inner diameter of the helix formed by the flat walls of the "D" is slightly less than the diameter defining the exterior surface of the heat transmissive wall whereby to grippingly position the helix thereon for final assembly and possible soldering.
A tubular helix formed in accordance with the method and apparatus herein advantageously allows large diameter tubing to be formed with rounded corner portions so as not to kink, such result reducing refrigerant flow and possibly providing less than a flat surface for optimum heat transfer. Further, the helix and deformed shape are formed simultaneously.
Other advantages and features of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.